Very high frequency radiating magnetron



June 1960 H. D. ARNETT 2,943,236

VERY HIGH FREQUENCY RADIATING MAGNETRON 5 Filed Aug. 31, 1959 s Sheets-Sheet 1 I A.0. POWER SUPPLY l9 w i I A.C. POWER SUPPLY I9 INVENTOR HENRY D. ARNETT ATTORNEY H. D. ARNETT 2,943,236 VERY HIGH FREQUENCY RADIATING MAGNETRON June 28, 1960 Filed Aug. 31, 1959 3 Sheets-Sheet 2 A.C. POWER l9 SUPPLY INVENTOR B HENRY D. ARNETT ATTORNEY June 28, 1960 H. 0. ARNETT 2,943,236

VERY HIGH FREQUENCY RADIATING MAGNETRON Filed Aug. 51, 1959 I a Sheets-Sheet :s

yIATION INVENTOR HENRY D. ARNETT ATTORNEY VERY HIGH FREQUENCY RADIATING MAGNETRON Henry D. Arnett, Washington, D.C., assignor to the United States of America as represented by the Secretary of the Navy Filed Aug. 31, 1959, Se1'.No.837,297

8 Claims. c1. sis-39.17

(Granted under Tifle 35, U.S. Code (1952), see. 266) t The invention described herein may 'be manufactured and used by or for the Government of the United State's a 19, although D.-C. currentrnaybe'used, while an electric of America for governmental purposes without the jpay- I rnent ofany royalties thereon or therefor.

This invention relates in general 'to magnetrons and in particular to a magnetron capable of generating electromagnetic wave energy having wavelengths of the order of 1 mm. and radiatingsuch energy directly into space.

In the field of centimeter and millimeter electromagnetic wave energy generation and radiation it has become increasingly diflicult to provide structures for generating electromagnetic wave energy having -the shorter wavelengths due primarily to the fine machine work-required 1 in shaping "the anodes of the magnetrons. With the high efiiciency of the magnetron, and its ability to generate large amounts of microwave power, it is desirable to extend the use of this device to electromagnetic energy having shorter wavelengths thereby providing means to advance progress in this field. The present invention avoids the disadvantages of prior art devices aiidfpro vides a' magnetron Whose anode can be fabricated with relative easeand which can be readily 'adapted'to radiate directly into space.

Accordingly, it is an object of this invention to provide a magnetron capable of generating electromagnetic wave energy having wavelengths of the order of one millimeter. It is another object of the present invention "toprovide 2 the anode. Apertures are omitted in one position or in more than one alternate positions with the section having one aperture where three or more "ordinarilywould be effecting radiation' into a space in selected direction; Referring to Fig. :1, envelope 11 isan evacuatedstruoe ture which surrounds anode 12 and hasextendingrthrough it leads to a cathode heater and "to the cathode,-neither of which is shown in this ffigure. Etched through :anode 12 are slots 13 which Fare uniform in :shape and spaced equallyaround the periphery of the dnQdfiWithdhefiiP,

ception of the positionsuindicated at 15 where slots are omitted. The heater-and cathode leads enter the .anode through insulator -16 which "also serves as a support tfor the cathode and attachments thereto. "The cathode heater is energized -by.A.-C. Tcurrent from A.-C. power supply field between anode 12.;and the cathode is established through power from DC. supply '18. A unidirectional magnetic -fie1d indicat'ed at B with an arrow in the direc:

tion-of the field is established by conventional means-mot shown in the drawings.

,,Fig.2 shows indetail theinterior of anode'12 in cross section. Cathode 21, which :is coated with :a suitable electron ernissive ;=material, "is shown within anode 12 supported in position by leads 23Fwhich serve the additional functions of supplying heating current to-thecathe ode heater, not shown in this figure, and energizing the cathode from D."C. power supply 18. Hatsfior, collars 22 are hollowed metallic cups which have a fitting, not shown in this figurefor purposes of simplification, extend ing from each'closed end toward and enclosing the-ends of cathode 2 1. Collars "22. are axially disposed within the anode such that facing edges Estare beyond the 6X1 trernities of a position on tlrecathodeestablishedby-radiallyzprojgectinganyslot to the cathode. The collars serve to restrain electrons y'from moving axially thus :insuring ama-gnetron'for millimeter wavelength energy generation whose anode can easily be fabricated.

It is a further object of this invention to provide a magnetron which can radiate 'dire'ctlyinto space.

It is a further object of the present invention to provide a magnetron for millimeter wavelength energy generation whose anode can easily be fabricated and which can radiate directly into space.

Other objects andadvantages ofthis invention will become-apparent upon a careful consideration of the following description when read in conjunction with the accompanyi'n'g drawings in which like reference numerals,

designate like parts throughout the figures thereof and wherein: p

Fig. 1 shows a schematicdiagramof 'a 'iirst iernbod-i ment of theinven-tion.

Fig. -2 a schematic diagramof some of the compone'rits depicted in Fig. 1.

Fig. 3 is a schematic diagram of components depicted in Fig.2.

Fig. 4- is a schematic diagramuoftheporjtiofn ofithfe l,

anode effectingradiation'into space.

In accordance with the teachings of the 'presentjinvem tion of self-radiating magnetron is provided which'l'is capable of generating electromagnetic energy-oft'he order of one millimeter in wavelengthand r'a-diatingthis energy intospace directly from the magnetron anode. The anode of the embodiment forradiatin'g'such energy'will consist primarily of molybdenum orftungsten sheeting fon'ned'into a'cylinder with an'arr'ay'of apertures equally spaceda'round asubstantial portion of "the periphery of that the electrons interact with the R.F."fields in -the vicinityof the anode. t j' 'Figx ll depicts construction details of icathode 21; andits position relative toanode slots 13. Tubular-fittings 25' of collars 22 atone end 'ofcathode 21 hold the'cathode in-position and at both ends thereof servewto deter'releetronsfrom moving in 'di-rectionsnot desired. An 'electric field E is established by energizingithe anodeand-cathode from D.-C. power supply 18. Heater coil 27 produces thermionic emission from .cathodeil upon being energized by power supply 19.

Fig. 4 shows in details the portion of the magnetron efiiecting radiation-intospace. Anode 12'is shown-insection alonga plane perpendicular to the axis thereof and bisecting the slots '13. The stream o felectrons indicated at A, having a pattern as shown which is explained hereinafter, approaches the anode in areas Where electroj magnetic wave energy indicated at 30 is opposite in direction to the stream of electrons while that -indicated at 31 is similar in direction to the electron stream. Areas indicated at-33and34sarel positions where slots have been omitted and'where'the radiation indicated at 35 occurs. It will be noted that the radiation at 35 extends a substantial distance from anode lzrduepri al i Fi marily to three successive fields having tion and complementing one another. H H In operation, cathode 21 is heated by A.-C. p or causing electrons to be emitted which are driven in a' I cycloidal motion bythe co'mbined magnetic fieldnindicated at B and electric field. indicated at E As the moving electrons approach anode '12 they will be either "retarded or accelerated according'to the direction of waves 30 0i" 31 they encounter. Those electronsencountering tin-0P1 I 2,943,236 Y Patented 1June'28, 1960 posing R.-F. electric field will be retarded and because of their reduced velocity the Lorentz force electrons will make many such interactions forming the wave-like effect indicated at A in Fig. 4 and finally arriving at the anode after having given up a substantial amount of their energy to the R.F. field. Those electrons encountering an accelerating R.- F.field will have their velocity increased thus increasing the Lorentz force tending to return them to the cathode. Because of the increased force the latter electrons will be driven into the cathode after one accelerating interaction and will abstract a negligible amount of power from the R.-F. field.

In the portion'of the anode where apertures are successive the electron stream is driven, under the influence of a D.-C. electric field and an axial magnetic field, in such a manner that opposing fields are excited in the apertures. In such portion of the anode, fields at successive slots are 180 out of phase with each other (qr-mode); Wheres-mode exists the fields of successive apertures oppose one another thereby preventing radiation away from the anode in such portions thereof.

Where alternate apertures are omitted the remaining apertures are driven in phase thereby permitting radiation at one aperture to complement and amplify that at another.

The array of apertures is resonant at a frequency for which the apertures are a half wavelength long and presents a high coupling impedance to a stream of electrons passing close to the apertures. A primary feature of the present invention is that wavelengths of the order of one millimeter may emanate from a structure in which the necessary narrow apertures are made within close tolerances by processes such as etching as compared with the more difficult process of fabrication required to shape anodes of prior art devices in this particular field.

The stream of electrons is controlled so as to move within the anode across the array of slots 13 therein. The slots will be resonant, and thus present a high coupling impedance to the stream when passing close thereto, at a frequency for which the slots are a half wavelength long. The nominal anode voltage for beam-slot interaction is given by the formula gauss where r =cathode radius r =anode radius N =number of slot positions Since successive electro-magnetic fields across successive slots are opposite in direction and therefore tend to cancel one another, self-radiation for a substantial distance is obtained by omitting one slot or more than one slot in alternate spaces around the anode. It may be shown that an array of slots of this nature will radiate me direction 0 with respect to the plane of slots according to the equation and since cos 021, no radiation will occur unless the electron beam will excite the conventional 1r-mode, for which'A=l, the structure can be prevented from radiating by making the 1r-mode section to excite the A=0 mode in the modified section. From Equation 3 it is seen that this section will radiate in a direction normal to the structure. The degree of coupling can be controlled by the number of omitted slots.

With such a source of millimeter wavelength available, studies heretofore not possible can be made. Some of these studies are experiments in the superconductivity of metals, diagnosis and measuring densities in fusion work and the determination of possible windows" in the atmosphere, i.e. frequency bands where atmospheric attenuation is relatively low. Advances in the field of communications can be considerable where the factors of flexibility, diificulty of detection, antenna size and antenna beam size are considered.

Many modifications and variations of the present invention are possible pursuant to the above teachings. It is therefore to be understood that the practice of this invention is not limited by the specific examples in the foregoing description nor by the theoretical explanation of its operation that has been presented. As an example, the anode may be of other material than that disclosed for the preferred embodiment. This invention is only to be limited by the scope of the appended claims.

What is claimed is:

1. A magnetron comprising an evacuated envelope containing an anode in the form of a hollow cylinder having a plurality of equal divisions which are equally spaced around said cylinder, a plurality of uniformly shaped apertures lesser in number than said plurality of divisions and having centers which are coplanar, each of said apertures positioned in the center of one of said plurality of divisions, said divisions without aperture being disposed at least one to each side of said divisions having apertures, means for generating a magnetic field extending axially through said cylinder, and means for developing a stream of electrons around the axis of said cylinder which interacts with said apertures such that said anode will resonate at a predetermined frequency.

2. A magnetron comprising an evacuated envelope containing an anode in the form of a hollow cylinder having a plurality of equal divisions which are equally spaced around said cylinder, a plurality of uniformly shaped apertures lesser in number than said plurality of divisions and whose centers are coplanar, each of said apertures positioned in the center of one of said plurality of divisions, said divisions without aperture being disposed at least one to each side of said divisions having apertures, and electron stream means including a source of electrons to excite said anode apertures at a predetermined frequency, said electron stream means including anode energizing means and a magnetic field to produce curvilinear motion of said electron stream and interaction of said stream with said apertures.

3-. A magnetron comprising an evacuated envelope containing an anode in the form of a hollow cylinder having a plurality of equal divisions which are equally spaced around said cylinder, a plurality of uniformly shaped apertures lesser in number than said plurality of divisions and whose centers are coplanar, each of said apertures positioned in the center of one of said plurality of divisions, said divisions without aperture being disposed at least one to each side of said divisions having apertures, means providing a source of electrons within the cylindrical space defined by said anode, and electric field producing means and magnetic field producing means for subjecting said electrons to the action of mutually perpendicular electric and magnetic fields such that a stream of electrons is produced which interacts with said apertures, said plurality of apertures shaped to resonate at a predetermined frequency, said disposition of said apertures in said divisions such that said predetermined frequency will be radiated unidirectionally along a line normal to said hollow cylinder.

4. A magnetron comprising an evacuated envelope containing and anode in the form of a hollow cylinder having a plurality of equal divisions which are equally spaced around said cylinder, a plurality of uniformly shaped apertures lesser in number than said plurality of divisions and having centers which are coplanar, each of said apertures occupying one of said plurality of divisions without aperture, said divisions without aperture being disposed at least one to each side of said divisions having apertures, electron source means including a cylindrical cathode axially positioned within said cylinder and extending a distance radially disposed from said apertures and substantially equal in length thereto, and means for developing a stream of electrons around the axis of said cylinder which interactswith said apertures such that said apertures will resonate at a predetermined frequency.

5. A magnetron comprising an evacuated envelope containing an anode in the form of a hollow cylinder having a plurality of equal divisions which are equally spaced around said cylinder, a plurality of uniformly shaped apertures lesser in number than said plurality of divisions and whose centers are coplanar, each of said apertures positioned in the center of one of said plurality of divisions, said divisions without aperture being disposed at least one to each side of said divisions having apertures, electron source means including a cylindrical cathode axially positioned within said cylinder and extending a distance radially disposed from said apertures and substantially equal in length thereto, a collar in the form of a metal hat positioned at each end of said cathode for restraining electrons from axial motion, and means for developing a stream of electrons around the axis of said cylinder which interacts with said apertures such that said apertures willresonate at a predetermined frequency.

6. A magnetron comprising an evacuated envelope containing an anode in the form of a hollow cylinder having a plurality of uniform apertures with the centers thereof coplanar about the circumference of said cylinder, said apertures having a slot configuration with the longitudinal axis of the slot substantially parallel to the axis of said cylinder, said circumference of said cylinder being divided into first and second sections, said first section having said apertures equispaced with a predetermined spacing therebetween, said second section having a plurality of apertures including a first aperture, a second aperture and a third aperture adjacent one another, said first aperture equidisposed between said second aperture and said third aperture at distances substantially twice said predetermined spacing, said second aperture and said third aperture disposed said predetermined spacing from respective next adjacent apertures in said first section, means providing a source of electrons within the cylindrical space defined by said anode, and electric field producing means and magnetic field producing means for subjecting said electrons to the action of mutually perpendicular electric and magnetic fields such that a stream of electrons is produced which interacts with said apertures, said plurality of apertures shaped to re sonate at a predetermined frequency, said spacing of said apertures in said second section such that said predetermined frequency will be radiated unidirectionally along a line normal to said hollow cylinder.

7. A magnetron comprising an evacuated envelope containing an anode in the form of a hollow cylinder having a plurality of uniform apertures with the centers thereof coplanar about the circumference of said cylinder, said apertures having a slot configuration with the longitudinal axis of the slot substantially parallel to the axis of said cylinder, said circumference of said cylinder being divided into first and second sections, said first section having said apertures equispaced with a predetermined spacing therebetween, said second section having 9 j a'plurality of apertures including a first aperture, a sec ond aperture and a third aperture adjacent one'another,

said first aperture equidisposed between said second aper-' ture andlsaid third aperture at'distances substantially' twice saidpredetermined spacing, said second aperture and said third aperture disposed said predetermined spacing from respective next adjacent apertures in said first section, electron source means including a cylindrical cathode axially positioned within said cylinder and extending a distance radially disposed from said apertures and substantially equal in length thereto, and means for developing a stream of electrons around'the axis of said cylinder which interacts which said apertures such that said apertures will resonate at a predetermined frequency.

8. A magnetron comprising an evacuated envelope containing an anode in the form of a hollow cylinder having a plurality of uniform apertures with the centers thereof coplanar about the circumference of said cylinder, said apertures having a slot configuration with the longitudinal axis of the slot substantially parallel to the axis of said cylinderg said circumference of said cylinder being divided into first and second sections, said first section having said apertures equispaced with a predetermined spacing therebetween, said second sectiond having a plurality of apertures including a first aperture, a second aperture and a third aperture adjacent one another, said first aperture equidisposed between said second aperture and said third aperture at distances substantially twice said predetermined spacing, said second aperture and said third aperture disposed said predetermined spacing from respective next adjacent apertures in said first section, and electron stream means including a source of electrons to excite said anode apertures at a predetermined frequency, said electron stream means including anode energizing means and a magnetic fiield to produce curvilinear motion of said electron stream and interaction of said stream with said apertures.

No references cited. j 

